The present invention is directed to an electronically commutated motor.
An electronically commutated motor is referred to in European Patent Application No. 0 732 801, which refers to a rotor containing a rotor position detector which detects a surface at where the rotor and stator poles diametrically oppose one another. A test current is applied simultaneously to all three phases of the electronically commutated motor, which may be a switched reluctance motor having three phases, six stator poles and four rotor poles. Due to the different coverage between the rotor and stator poles, the inductance in at least one phase differs from that in the two other phases. The inductance influences the rate of current rise of the test current, which is detected in all three phases. The rates of current rise corresponding to the inductances are compared with three predetermined signal level classes and classified accordingly. Based on the principle of measurement and the geometric relationships between the surfaces located between the rotor poles and stator poles, such position detection makes a precision of 15xc2x0 possible, which may be adequate to determine the phase to be supplied with current for the starting operation of the motor.
The object of the exemplary embodiment and/or exemplary method of the present invention is to provide an electronically commutated motor having a rotor position detection which offers a high level of precision.
In the electronically commutated motor according to the present invention, the entire surface at which the rotor and stator poles diametrically oppose one another is considered in the position detection. In doing so, the pole angles of the rotor and stator poles are always to be set to values at which a rotor rotation results in a surface change.
The exemplary embodiment and/or exemplary method of the present invention makes the rotor position available with high precision within an angular range of rotor rotation. The angular range of rotor rotation is a function of the number of poles of the rotor. In a four-pole rotor, it is sufficient to determine the position within a angular range of 90xc2x0. In a six-pole rotor, 60xc2x0 is sufficient. Within these angular ranges of rotor rotation, its possible to make a rough position determination using, for example, the device of the related art. In doing so, a precision of xc2x115xc2x0 is achieved in a three-phase motor having six stator poles and four rotor poles. Within this angular range, the exemplary embodiment and/or exemplary method of the present invention increases the precision to less than 1xc2x0. The pole angles of rotor and stator poles may be determined either experimentally or by using tables. The values at which a maximum surface change occurs during a rotor rotation may be selected.
Exemplary embodiments of the electronically commutated motor and/or exemplary method according to the present invention are described herein.
According to one exemplary embodiment, the rotor pole angle is identical to the stator pole angle. Aside from the advantages from the point of view of the magnetic flux, this embodiment may have the advantage that the determination of the pole angle of the rotor and stator poles is simplified.
According to an exemplary embodiment, the stator includes at least two parts and that the measurement of capacitance between the at least two stator parts is used to determine the position. The capacitive coupling occurs at the stator segments produced by dividing the stator and also at the position-dependent overlapping surfaces between the rotor and stator poles.
According to an exemplary embodiment, the inductance of the total system composed of the rotor and stator is detected. In this connection, at least some poles (which may be all poles) of the rotor contain a sensor winding. All windings may be connected in series.
Another exemplary embodiment provides the combination of capacitance and inductance measurement. The inductance and the capacitance are interconnected to form an oscillating circuit, a series oscillating circuit, for example. A variable frequency generator excites the oscillating circuit, the oscillating circuit voltage being detected. A change in frequency of the variable frequency generator makes it possible to determine the resonance frequency of the oscillating circuit, which is a measure of the position of the rotor.
The electronically commutated motor of the present invention is implemented, for example, as a switched reluctance motor, which has a robust structure since the rotor contains no additional electrical component.
Other exemplary embodiments of the electronically commutated motor according to the present invention are described herein.